Gravure cylinders or printing rollers used in rotary printing processes generally consist of a cylindrical metallic core on which is electroplated an image-carrying copper layer and a protective outer chrome layer. After a printing run or expected production life of the cylinder roller, it is known to refurbish the cylinder for re-use. Conventionally, gravure cylinders are refurbished by precision grinding the outer surface of the cylinder to remove just the outer image-carrying copper and chrome layers from the metallic core. The copper layer is then reapplied directly onto the metallic core and a new image is engraved or etched into the copper layer. Finally, the outer protective chrome layer is reapplied directly onto the image-carrying copper layer. A difficulty exists with such a refurbishing process in that refurbished cylinders are dimensionally restricted by the outer diameter of the metallic core, such that the refurbished cylinder rollers may not be re-used in applications requiring larger diameters cylinders. Additionally, after successive refurbishments, the cylinder wall of the refurbished cylinder becomes thin, thus reducing the structural integrity of the cylinder.
In an alternative method for refurbishing cylinder rollers after grinding, polyurethane is molded around the metallic core, cured and subsequently sized on a lathe. A ceramic coating layer is then applied to the outer circumference of the polyurethane layer and after which time the roller is further machined on a lathe to size to a desired outer diameter. Following sizing, a layer of nickel paint is applied over the ceramic coating layer. Copper is then plated directly onto the nickel painted layer. The copper layer is engraved with an image, after which a final protective chrome layer is applied over the image-carrying copper layer.
The applicant has appreciated that in applying a nickel painted layer, surface defects and surface thickness variations often lead to defects in the quality of prints made by cylinders refurbished by this process. In particular, as a result of the painting process, the thickness of the nickel paint layer is typically not uniform across the ceramic coating layer. In addition, surface scratches often arise in the nickel layer during handling of the cylinders. These defects affect the quality of the electroplated copper layer and subsequently result in inferior quality printings. Additionally, resizing requires the cylinder to be returned directly to the manufacturer, where the coating layers including the nickel paint layer must be reapplied using specialized equipment.